1. Field of the Invention
The present invention relates to a screening method for conducting tensile strength tests of an optical fiber, a wire or the like by applying a load thereto and an apparatus for carrying out the method.
2. Description of the Related Arts
In the manufacturing line of an optical fiber, in order to guarantee the breakage longevity of the optical fiber, a proof test is conducted. In the test, a weak portion of the optical fiber is broken and removed by applying a certain tensile force to a part of the manufacturing line. The test is conducted by using a screening apparatus.
A conventional screening apparatus is described below with reference to FIGS. 16 and 17. FIG. 16 shows a schematic construction of the conventional screening apparatus. FIG. 17 is a sectional view taken along a line 17--17 of FIG. 16.
The apparatus comprises a feeding roll 1 for feeding out a drawn optical fiber 2; a capstan wheel 3, around which the optical fiber 2 is wound, for supporting the optical fiber 2 by means of a capstan belt 4; a screening roll 5; a tension roll 6; a winding roll 7 for winding the optical fiber 2 to which tension has been applied by a torque between the capstan wheel 3 and the screening roll 5; an arm type feeding dancer 8 provided between the feeding roll 1 and the capstan wheel 3; an arm type winding dancer 9 disposed between the tension roll 6 and the winding roll 7. The feeding dancer 8 and the winding dancer 9 absorb the fluctuation of speed and tension of the optical fiber 2 between the capstan wheel 3 and the feeding roll 1 and between the capstan wheel 3 and the winding roll 7.
According to the screening apparatus, the optical fiber 2 is fed out from the feeding roll 1 and tension is applied thereto between the capstan wheel 3 and the screening roll 5, then, wound around the winding roll 7. The line speed is determined by the drive of the capstan wheel 3. The feeding dancer 8 and the winding dancer 9 absorb the fluctuation of speed and tension between the capstan wheel 3 and the feeding roll 1 and between the capstan wheel 3 and the winding roll 7. Tension is applied to the optical fiber 2 between the capstan wheel 3 and the screening roll 5, and the optical fiber 2 is broken at a low strength portion thereof. Thus, the low strength portion of the optical fiber 2 is not wound around the winding roll 7.
Owing to the screening test, the low strength portion of the optical fiber 2 is not wound around the winding roll 7. But it is necessary to manually install the optical fiber 2 on the path line again. Japanese Patent Laid-Open Publication No. 62-91441 discloses that the optical fiber can be manually mounted on a path line easily by reciprocating a guide roller during drawing process which is required to be continuously operated for a certain period of time.
According to the conventional screening apparatus, the low strength portion of the optical fiber 2 is not wound around the winding roll 7 because the optical fiber 2 is broken at a low strength portion thereof owing to the screening test. But winding operation is suspended when the optical fiber 2 is broken. Therefore, it is necessary to mount the optical fiber 2 on the path line manually when the optical fiber 2 has been broken. It is necessary to automatically mount the optical fiber 2 on the complicated path line by gripping the optical fiber 2 after it is broken at the low strength portion. It is particularly difficult to automatically mount the optical fiber 2 on the winding dancer 9 because the optical fiber 2 needs to be turned plural times as shown in FIG. 17 so as to absorb the fluctuation of the speed and tension of the optical fiber.
In addition, it is necessary to suspend the operation or manually rewind the optical fiber in a subsequent process in order to remove a defective portion other than the low strength portion, such as a random thickness, a bubble-mixed portion, a different-diameter portion or an abnormal projection. Thus, the operation is inefficiently performed.